The invention relates to a guide rail for a cable or Bowden cable window lifter according to the preamble of claim 1 and to a method for manufacturing a guide rail for a cable or Bowden cable window lifter according to the preamble of claim 20.
Metal guide rails for cable window lifters are known where the surfaces are coated at least in part and which are a constituent part of a window lifter assembly structure which has to be assembled and fitted accordingly. Depending on the metal used and the number and type of joining and assembly processes the window lifter assembly structure manufactured in this way is relatively heavy. As a result of each of the manufacturing processes used for the individual parts and where necessary the surface coatings and as a result of each joining and assembly process used the risk of errors is considerably increased which can have a negative effect on the quality of the window lifter.
As a result of the relatively expensive manufacturing processes and thus the expense connected therewith for development and quality control the manufacturing costs are high. Furthermore as a result of the unfavourable friction pairing between the metal surfaces of the guide rails and the slide members for guiding the window pane it is also necessary in addition to lubricate the contact surfaces and where applicable to coat the guide rail.
From DE 41 31 098 C1 a guide rail is known for a cable window lifter where the guide areas are provided at the same time for fixing the guide rail on the door inside panel. For this purpose a fixing bolt is passed through the cable pulley, e.g. a cable roller, and is connected to the door inside panel. The force flow can thereby be introduced directly into the door bodywork without deflection through the guide rail so that the guide rail need mainly undertake the guide tasks and the transfer of transverse forces when closing the door. In this connection it is proposed to replace the guide rails of metal which have been used up until now by plastics guide rails. Further details on the structural design of plastics guide rails are not provided.
From EP 0 561 440 A1 an assembly support for assembling a window pane and a window lifter in a vehicle door is known which is made in one piece from plastics and which has a central fixing plate for holding the window lifter and several hollow spokes extending star-fashion from the central fixing plate and connected to this in one piece. The ends of the spokes are likewise provided with integral guide channels for holding the edges of the window pane. The hollow spokes have several fixing clips connected integral therewith and serving to fix the assembly support on the vehicle door.
The window guide channels for holding the window pane edges are defined by spaced side walls which consist of several brackets extending from a base and arranged off-set from each other on alternate sides. A slide strip of an elastomer is inserted in the window guide channels between the brackets in order to improve the sliding properties when guiding the edges of the window pane. As an alternative it is proposed to make the window guide channels from separate plastics material or from metal slide strips which are fixed in a suitable way at the ends of the hollow spokes of the assembly support. The required stiffness of the known assembly support is produced by the shape of the hollow spokes and by cross ribbing of the central fixing part.
The known plastics assembly support has a complex shape which can only be manufactured at considerable expense by observing close manufacturing tolerances. The known assembly support can only meet to a limited extent the requirements for the stability and guide properties which are required by a window lifter module, so that additional measures are necessary in order to increase the rigidity and to improve the sliding properties in the guide channels serving to hold the window pane.
From U.S. Pat. No. 4,835,907 a guide rail is known for a window lifter which has a longitudinally extended guide area for guiding a cable and which is provided at each end of this guide area with a deflection area for the cable guided in the guide area. These deflection areas serve to deflect the cable to a drive. In each of the deflection areas the cable is guided in a curved groove in which a plastics element is additionally inserted in order to improve the gliding properties. The deflection areas moreover serve as fixing areas for fixing the guide rails on a vehicle door and have reinforcement elements.
In EP 0 385 167 A1 a cable deflection member for a Bowden cable window lifter is described which is fixed at the ends of a profiled rail made from metal or plastics and which has an angled side wall for reinforcement.
The object of the present invention is to provide a guide rail and a method for manufacturing a guide rail for a cable or Bowden cable window lifter of the kind mentioned at the beginning which are adapted for using plastics as the material for at least a part of the guide rail.
This is achieved in respect of the guide rail by the features of claim 1 and in respect of the manufacturing process by the features of claim 19.
According to this at least the guide area of the guide rail consists of plastics and the guide rail has a separate reinforcement area with reinforcement elements connected to the guide area wherein the reinforcement area extends in the longitudinal direction of the rail at least over the middle section of the guide area and also encloses the fixing area of the guide rail.
Since the guide rail consists in part or completely of plastics and as a result of the structural division of the guide rail into a guide area which mainly undertakes the task of a slide guide, and a reinforcement area which ensures the required bending and torsion strength and mainly undertakes the mechanically supporting functions of the guide rail, the guide rail can be designed so that it has low weight and low manufacturing costs.
Through the now possible integration of several functions which hitherto were mostly produced from several individual parts which then had to be assembled, the risk of errors can be eliminated or reduced and the quality of the structural unit overall is improved.
The design of a guide rail according to the invention for a cable or Bowden cable window lifter is suitable both for the mechanical stresses of a guide rail in relation to the bending and torsion rigidity and also the tribological demands on a guide rail with regard to the abrasion strength, good sliding properties for guiding the pane and the lowest possible noise development.
Since the guide rail (more particularly its guide area) is made at least in part of plastics there is a greater freedom when designing the plastics parts. By matching tribologically particularly suited friction pairings of plastics between the guide area of the rail and the slide member for guiding the window pane there is the possibility of using this friction pairing without additional lubrication and of improving the product economically and technologically.
The reverse sides of the slide faces of the guide area are preferably not directly connected to the reinforcement elements so that the necessary but also adequate separation between the guide area and the reinforcement area is ensured. Reinforcement elements can thus be arranged in all areas of the guide rail, only not in the area of the slide faces, i.e. in the area of the path of the window pane follower. The front side of the guide faces or areas thereby forms the contact with the window pane followers or sliders.
The reinforcement elements preferably consist of ribs and/or webs which are formed on a surface of the reinforcement area preferably integral and substantially perpendicular to the surface of the reinforcement area. The ribs and/or webs can be formed in particular as waffle pattern or as cross ribbing. Alternatively the reinforcement elements can consist of hollow profiled sections.
A favourable stiffness/mass ratio is reached through the arrangement of reinforcement elements, such as ribs, webs or hollow profiles, in the reinforcement area.
Preferably ribs and/or webs extending like rays from the force introduction points are arranged around the force introduction points, for example in the area of the fixing points for connecting the guide rail to an internal panel, a door module or the like and/or about fixing points for additional component parts such as window lifter motors, cable pulleys or the like.
The forces emanating from the fixing points are thereby introduced directly into the cross rib structure of the reinforcement area so that the stability of the guide rail is also guaranteed at these necessary weak spots.
By dividing the guide rail into a reinforcement area and a guide area the prerequirement is provided so that the reinforcement area can be made from a plastics with high mechanical strength and the guide area can be made from a plastics with good tribological properties, whereby both areas can be connected integral together and thus produce one structural unit. By manufacturing the guide rail in the twin- or multi-component injection casting process it is possible to divide the guide rail into a reinforcement area with a material of high strength and high E-modulus and a guide area with webs, ribs or guide elements of a tribologically favourable material which has optimum low friction values, low wear and low noise level.
The guide and reinforcement functions are thus structurally separated whereby the guide area (which can be pressed, cast or drawn from plastics with particular advantage) can be made without reinforcement elements and can be spatially separated from the areas subjected to higher mechanical stresses (reinforcement area), with only the reinforcement area being provided with reinforcement elements.
It has thereby proved advantageous to connect the guide area with the reinforcement area through a short lever arm and to select a greater material thickness at least for some parts.
The reinforcement area is preferably designed on the principle of a bending support structure and has additional plastics-reinforcing fibres, more particularly glass or carbon fibres. By way of example the middle part of the reinforcement area has a larger cross-section than the ends.
In the case of a combination of a plastics guide rail with a metal profile the reinforcement area of the rail is made from metal whilst the guide area is made from plastics owing to the better tribological properties. The reinforcement area thereby consists of a metal profile with favourable mechanical properties and is characterised by a high resistance moment with a relatively light weight. The guide area which is made of plastics is connected with keyed and/or force locking engagement to the metal profile, for example by completely or partially overmoulding the metal profile which forms the support structure, through co-extrusion of the plastics on the metal profile or through subsequent joining of the plastics and metal through adhesive, welding, clips or push-fit connection.
When injecting plastics round the metal profile the plastics can in addition to the guide function also contribute to a deliberate additional strengthening of the metal profile whereby ribs and reinforcements produce a hybrid structure which is resistant to both bending and torsion. In this way a simple bending-resistant metal profile can be made with plastics ribs or plastics structure into a torsion and bending resistant function element.
Furthermore the metal profile can be fitted into a channel of the plastics body of the guide rail. Alternatively a plastics structure can be injected onto the bending-resistant metal profile in order to improve the torsion resistance. Since for example a U-profile is not very resistant to distortion, by injecting a plastics structure onto same the profile becomes resistant to distortion although the plastics itself is being used in particular on account of its good tribological properties.
The guide areas in the form of guide webs, ribs or guide elements can be coated with an anti-friction paint or can be vacuum- or plasma-coated with a suitable substrate, for example by means of plasmaxe2x80x94CVD coating in order to improve the tribological properties. The anti-friction paint can thereby also be used on the plastics when the plastics has a particularly good bearing capacity with good mechanical strength properties but does not have particularly good tribological properties.
An improvement to the tribological properties as well as also to the mechanical properties can be achieved by cross-linking the molecular structure of at least the surface of the material used, for example through the action of suitable chemical means or through ionising radiation, more particularly gamma radiation. A thermoplastics material is thereby changed at least in part into the duroplastics state.
The strength and stiffness of the plastics rail can be further improved by using special tool and method techniques, for example by using a cascade casting system, which avoids undesired binding seams, or through counter-beat injection casting with fibre-reinforced or LCP materials, whereby a strengthened orientation of the molecular structure and thus a higher E-modulus is obtained.
As opposed to the continuous metal profile, the reinforcement area can be shaped so that the cross-section is suitably configured over the length according to the bending moment which occurs.
In order to manufacture the plastics rail it is possible, particularly when using thermoplastics reinforced with oblong glass fibres, to use an injection stamping or gas internal pressure process so that the material properties can be utilised in the best possible way and manufacture is achieved with little distortion.
In order both to make the plastics rail mechanically rigid and nevertheless to produce on the surface the most favourable surface condition for friction pairing all without any expensive tool technology, it is advantageous to use the 2-plastics injection in the overmoulding process. The surface, more particularly the guide area exposed to the tribological strain, can thereby be formed by unstrengthened material whilst the core is formed by a fibre-reinforced material.
Flexible areas can be arranged at the transitions between the reinforcement area and the fixing points of the guide rail in order to provide compensation for the length and/or angular tolerances and where necessary any existing thermal expansion differences between the guide rail and the door structure.
The guide rail can integrate as a plastics component part further adjoining component parts or their functions. These can be for example a base plate, a bearing cover, bearing spots and fixing spots. The guide rail can be a constituent part of a larger door module, which integrates further functions, such as for example a door lock, door electronics and sealing functions.
Further integration possibilities are injection moulding the guide pulleys with subsequent rotatable bearing in the 2-plastics process. A pre-requisite for this is the fixing, for example riveting or screwing of the rail on the door structure at the bearing points of the guide pulleys.